This invention relates to ink jet printing in general and, in particular, to continuous jet printers. Such devices are used for high speed marking of alpha-numeric characters on a variety of substrates including consumer products which require date codes, for example. Continuous jet systems operate by deflecting selected drops of ink onto the substrate to be marked while returning the unused drops to the print system for reuse. As the ink is consumed, it is necessary to provide fresh ink to the printer. In addition, it is periodically required to provide replacement solvent to compensate for losses due to evaporation thereby to keep the ink composition relatively stable.
Accordingly, in most ink jet systems, there is provided a solvent container from which the system draws solvent when required and a separate ink container from which fresh ink is drawn as needed. The printing system itself typically contains a micro-processor based controller which employs various techniques to measure ink composition, quantity, viscosity and/or temperature to determine when solvent and/or fresh ink needs to be added. When the need is detected, valves are operated to draw solvent or ink or both from the containers into the ink operating system.
One example of such a system is disclosed in U.S. Pat. No. 4,555,712 to Arway assigned to the present assignee. In this patent, as shown in FIG. 2, there is a solvent container 58 and a fresh ink container 56 operated by an electronic controller 34 to add supplies to the ink jet system. A greatly simplified illustration of such a printer system according to the prior art is shown in FIG. 1 of the present application.
While the two container system works quite well in practice, there are certain disadvantages. Maintenance activities are frequent because the ink and solvent are typically consumed at different rates and thereby require replenishment at different times. A related problem is the need for users to stock and handle two different supply products for the same machine. In that connection, because the containers typically are physically the same but labeled differently, it is possible to inadvertently interchange the connections to the printer system so that solvent is drawn into the system when ink has been requested and vice versa. Such a mix-up causes faulty operation and down time for servicing of the printer. Another problem with a two container supply system is the potential spilling of liquid ink during installation. The present invention is an improvement over prior art systems which use two supply containers in that a single volume of solvent is used to create fresh ink and for solvent replenishment.
It has been suggested in the prior art to provide a single supply system for drop-on-demand ink jet printing. Such a system is disclosed in European Patent application No. 941 068 14.0 to Due published Mar. 15, 1995 (Publication Number 0642924A2). The Due application discloses, at FIGS. 1 and 2, a housing having a collapsible ink concentrate container provided therein. Fluid, preferably water from a water supply, is introduced into the housing to apply pressure to the ink concentrate container. Concentrate is forced from the container to a mixing manifold forming a portion of the housing. At the manifold, the water and ink concentrate are mixed and thereafter supplied to an ink jet printer. In the embodiment shown in FIG. 4 of Due, a switchable system is illustrated in which an empty system can be replaced without interrupting printing.
The present invention is an improvement over Due in several important respects. Due appears to be limited to installations employing a pressurized fluid supply, i.e., a water supply. Further, this device provides only fresh ink, not a separate supply of solvent because it is intended for a drop-on-demand printing system not a continuous jet system. Thus, it lacks any provision for solvent to make up for evaporative solvent losses.
It is accordingly an object of the present invention to overcome these and related problems and to simplify the method of providing solvent and fresh ink to the printer system.
It is a further object of the invention to provide a system whereby an ink jet printer can be operated over extended periods of time by periodic replacement of a single, integrated supply containing both solvent and fresh ink.
It is a further object of the invention to produce fresh ink on demand to avoid ink spills or spoiling or contamination before use. These and other objects of the invention will be apparent from the remaining portion of the specification.